You can now use your Flint app for the iPhone to process American Express and Discover card payments in addition to Visa and MasterCard. The free app lets you accept credit card payments on your Apple smartphone.

The transaction fees to process AMEX and Discover cards are the same as Visa and Mastercard. Plus, accepting all major credit types brings you more flexibility and sales. Per transaction fees are 1.95% for debit cards and 2.95% for credit cards, same for card scan, manual entry, invoices or online payments.

Flint's technology securely scans the card number off the credit card. The app doesn't take a photo of the entire card or save an image on the phone. It supports keyed number entry as a backup option.

With the Flint app, you can create, send and track invoices to your customers from the mobile app or online merchant portal. Your customers will receive an emailed invoice with a "Pay Now" link they can use to pay online with a credit card. Reminders are sent automatically to your customer.

The Flint app also allows you to sell items online and receive secure payments from customers by adding "Buy Now" buttons to your web site or sending e-commerce links to your customers via emails or social feeds.